Logging and monitoring boreholes has been done for many years to enhance and observe recovery of oil and gas deposits. In the logging of boreholes, one method of making measurements underground includes attaching one or more tools to a wireline connected to a surface system. The tools are then lowered into a borehole by the wireline and drawn back to the surface (“logged”) through the borehole while taking measurements. The wireline is usually an electrical conducting cable with limited data transmission capability. Similarly, permanent monitoring systems are established with permanent sensors that are also generally attached to an electrical cable.
Demand for higher data transmission rates for wireline logging tools and permanent monitoring systems is growing rapidly because of higher resolution sensors, faster logging speeds, and additional tools available for a single wireline string. Although current electronic telemetry systems have evolved, increasing the data transmission rates from about 500 kbps (kilobits per second) to 2 Mbps (megabits per second) over the last decade, data transmission rates for electronic telemetry systems are lagging behind the capabilities of the higher resolution sensors. In fact, for some combinations of acoustic/imagining tools used with traditional logging tools, the desired data transmission rate is more than 4 Mbps.
In addition, while higher data transmission rates are desirable, many tools in current use would have to be completely reworked or replaced to incorporate new data transmission technologies. It would be desirable to facilitate faster data transmission rates with minimal changes to existing tools and equipment.
Furthermore, oilfield application of fiber optics sensors has been progressing in recent years for monitoring of certain parameters. However, many downhole applications require high temperature operations, and optical devices such as laser diodes degrade rapidly or do not operate properly at high temperatures. Therefore, use of fiber optics for communication between surface systems and downhole tools, as well as use of downhole sensors, in high-temperature conditions, within a borehole, has been limited.